A. Field of the Invention
The present invention is related to electromagnetic locking systems for locking and unlocking access means such as doors, drawers, etc. and more particularly to a system and method for controlling a set of bi-stable solenoids for battery powered or low power electromagnetic locking systems comprising the use of a capacitor to provide the correct voltage amplitude for the release action of the solenoid and the separation of the battery from the solenoid at the actuation moments, thus eliminating instant high power requirements to the power source.
B. Description of Related Art
A bi-stable solenoid is a device that requires power to change its state but not to hold it. This is ideal for low power applications because it eliminates the need to provide power for holding a particular status (i.e. unlocking a mechanism). This is also very important because some applications require that a particular status be maintained during undetermined periods of time (i.e. unlocking a door for a certain period of time.)
A bi-stable solenoid requires two important control parameters, polarity and voltage amplitude. For example, if the bi-stable solenoid is used In a locking system for retracting (which comprises a “retracted” or unlocked status) or release (which comprises a “released” or locked status) a plunger, it is necessary that a full rated “positive” polarity power amplitude be provided to the solenoids by a driving circuit in order to change the status of the system to “retracted”. In order to change the status of the system to “released”, the driving circuit needs to provide a lesser “negative” polarity power amplitude. The exact difference between the “retract” and “release” power amplitudes varies with each different application and varies depending on solenoid construction.
A typical control system for a bi-stable solenoid consists of four transistors configured to provide power in either “positive” or “negative” polarity. Such circuit is commonly referred to as an H-bridge, which requires the control circuit to connect a first and a fourth switch for one polarity and a second and a third switch for the reverse polarity.
A control circuit must be provided for each solenoid that the system must control; this requires a great amount of driving lines from the controller and introduces a parasitic power requirement from every transistor.
Additionally a regular driving circuit is needed to change the voltage amplitude for the second polarity in order to provide the bi-stable solenoid with the adequate amount of voltage to release its plunger.
Furthermore, when the locking system main power source comprises a low power source such as a battery or solar cells, the power requirements during instant surges of power required from the locking system, may not be completely supplied by said low power sources or can have adverse effects such as quick battery degeneration, excessive noise on the power supply lines).
In view of the above referred problems, applicant developed a system and a method for controlling a set of bi-stable solenoids for locking applications which eliminates the direct connection of the power supply and solenoid by introducing a capacitor and a switch between the power supply and solenoid. Additionally it eliminates the need of a dedicated h-bridge for every solenoid, thus reducing the control lines required for each solenoid such that after the initial control lines, every subsequent solenoid requires only one control line to select the appropriate solenoid.